View Full Version : POI shift through over-caliber suppressors
I'm looking at picking up a brake attached Ti suppressor (in 30 cal) with the intention of moving that can between a 260 rifle (KMW-LRS 260 or an LT PredatAR rebarreled in 260) and an eventual 300BLK SBR.
For removal/reinstallation on the precision rifle, is POI shift something I need to be really concerned about using the manufacturer muzzle brake/thread on attachment?
Should I be looking at the more expensive of the two units based on the POI shift?
Right now I'm comparing between the more affordable SAS-LLC Arbiter and the TBAC 30-BA
POI shift is a product of one thing:
Barrel harmonics being changed by a weight being hung off the end of the barrel.
You could argue a secondary effect caused by harmonic resonance due to the hollow chambers... but you'd need a lab to test it and wouldn't be applicable in the real world.
This is clearly illustrated by the fact that lighter suppressors exhibit less POI shift than heavy ones, as a rule.
Proof? Take a straight barrel with no taper, at about 18" in length and hang a 2lb suppressor off the end. It will likely not shift POI at all. Now hang the same suppressor off a 24" sporter barrel.
However this is not a constant, as all barrels will resonate slightly different depending on the barrel and the load used. This is the same principle we use to tune loads to our barrels, and is also why I do load development with the suppressor on, if the rifle is primarily to be shot that way.
There is a bit more to it, but that is the nuts and bolts of it. POI shift with any suppressor and any rifle, will generally be consistent and repeatable... thus - easy to account for.
Anchor Zero Six
11-10-11, 10:38
POI shift when changing harmonics is a given as orkan stated.
Whats important is that its a consistant shift meaning repeatable and replicatable.
Both of the cans you are looking at have good reputations so I would say you would be GTG either way.
You should keep data on the zero for both supressed and unsurpressed. An example of application would be that you zero the rifle unsurpressed first. Attach the can rezero and log how many mils of correction were dialed. Do this several times and average the correction.
I would also advise to do this over several firring sessions at varying temps and altitudes. If you have enough data in your log books you can predict your cold bore shots with a surprising degree of accuracy. Just takes a while to get the data but who cares its an excuse to go shoot right?
http://www.gregd.net/pics/funny/Threadjack.jpg
If you have enough data in your log books you can predict your cold bore shots with a surprising degree of accuracy.
I've yet to see any change in POI from cold bore, to 5th shot in any of my rifles. Have you proven cold bore differs for yourself, or have you just read about it?
I'm convinced its a matter of cold shooter much more so than cold rifle. I've not had anyone show proof of otherwise.
Want a test? Take two similar rifles that you know to exhibit excellent accuracy. Shoot one for 20rnds or so until you are warmed up and comfortable. Then swap the rifles. See if your POI is really any different with the other rifle. In my experience, this proves cold bore to be a myth. Granted, not many people have two rifles with identical stocks and triggers to replicate the same feel... but some do. I've done this test on several people, and it always ends the same. Cold bore doesn't exist... but cold shooter does.
One of the best ways to overcome it, is to get in position, and dry fire about 5-10 times on target until you are comfortable in the fundamentals and verify that you have built a solid position. This is especially helpful when shooting heavy recoiling rifles.
Now, there is one factor that is often overlooked. Shooting sessions never have the same environmental conditions as the one previous. So another thing that people attribute to POI shift is actually changing environmental's which affect their zero, yet were unaccounted for during the shot. Most people don't shoot enough to truly track this phenomenon. Want another test? Shoot your rifle at 300yds, 5 shots, every single day... for a month. Record all data... and compile it for eval at the end of the month. You really want to learn something about yourself and your rifle, this is one very efficient way to do it.
Driving a rifle properly, like any motion where precise repetition is key, is always done best after a bit of practice during each session. This is a fact. The only way to get rid of it, is to train it away through repetition.
Anchor Zero Six
11-10-11, 13:21
Some good points there and I agree with them. I think my wording was poor or rather upon consideration the term itself is missleading. I have never thought about the literal definition of the term cold bore and always took it to mean the first shot fired.
I think you nailed it by saying cold shooter and enviormental conditions. What I was getting at is knowing what corrections need to be made to get a first round hit at the start of a new day of shooting (possibly at a different location).
And no I have not seen evidence of "cold bore" shots differing from others throughout the day in regards to accuracy (moa) but I have seen variations in point of impact vs point of aim. POI vs POA obviously attributed to changes in enviorment. This is assuming a normal rate of fire as I think all have seen hot barrels walk.
On of my prefered shooting drills is the Dot drill and the very first round fired is a "cherry popper" for the reason you mention its gets you past the cold shooter stage.
I've yet to see any change in POI from cold bore, to 5th shot in any of my rifles.
What about CLEAN bore? We cleaned bores mid day in a precision class I took years back. .(223 Rem 700 with a Shilen bbl) And it took 3 rounds for the POI to get back home.
Now My Rem 700 will shoot clean cold bore absolutely perfectly. I mean it's first shot is sometimes the best shot of the day.
What about CLEAN bore?
IMO, this a whole new discussion. IMO, cleaning midway through a course of fire is asking for misses or poor accuracy until the bore is fouled up and the natural imperfections are filled smoothed over with carbon and copper.
IMO, this a whole new discussion. IMO, cleaning midway through a course of fire is asking for misses or poor accuracy until the bore is fouled up and the natural imperfections are filled smoothed over with carbon and copper.
This.
My rifles are always in a "fouled" condition. My custom barrels take as little as 3 rounds to come in, after being cleaned... while most of my factory barrels will take from 10-20.
This.
My rifles are always in a "fouled" condition. My custom barrels take as little as 3 rounds to come in, after being cleaned... while most of my factory barrels will take from 10-20.
Same reason mine is fouled up too. We're on the same page!!!!
I've drawn the ire of plenty of my armorers by refusing to clean the barrel during our qual week, and my old issue rifle was a real tack driver if I kept the bore flithy.
I'm guessing ambient temperature will probably have some effect on zero, but I doubt it'll be terrible pronounced between suppressor on and off.
To a degree I feel like the AAC MITER multi-ratchet system was gimmicky from the start (shouldn't all cans be radially symmetrical unless they're really half-ass?), but the brake with thread-over should give me fairly consistent results, so I'll work with that.
I'm also assuming that going Ti will also help with this.
As far as figuring out the various shifts across conditions and loads, I'm working on a pretty detailed statistical DOE setup that I think can minimize cost and improve load development as well as give residual information about POI shift and temperature effects on loads.
To directly answer your question, I've not seen any difference in POI shift on an over-caliber suppressor.
On my DTA I run a YHM 338 can on every barrel. Shift is approx half a mil on the 338 barrel, and about 2 tenths on the 308 barrel. The 308 barrel is shorter and thus stiffer, and that is what I attribute the difference in shift to.
IMO, this a whole new discussion. IMO, cleaning midway through a course of fire is asking for misses or poor accuracy until the bore is fouled up and the natural imperfections are filled smoothed over with carbon and copper.
That was the entire point of the excersize. We cleaned and then watched our poi walk back to zero.
That was the entire point of the excersize. We cleaned and then watched our poi walk back to zero.
My bad. I wasn't aware that it was done as part of a teaching point. I know some old timers clean the barrels as a result of old ways, and no other reason.
R.
As long as the POI shift is repeatable you are good to go.... If its not then thats another story. Typically thread on cans are usually better for precision if thats what you are looking for compared to QD models
As long as the POI shift is repeatable you are good to go.... If its not then thats another story. Typically thread on cans are usually better for precision if thats what you are looking for compared to QD models
Can you provide any first-hand proof of that statement? ... or are you just regurgitating something you read somewhere?
Just over 700yds, with a QD YHM 7.62. 5 shots.
http://www.gregd.net/pics/guns/range_report/2010/IMG_0154.JPG
About 1050yds with the same: 10 shots. 8 hits I think.
http://www.gregd.net/pics/guns/range_report/2010/IMG_0140.JPG
3" target at 400yds using a DTA with 308 barrel, with a QD YHM 338 suppressor.
http://www.gregd.net/pics/guns/targets/IMG_2664.jpg
Hardly my best work, but these pics were quickly accessible. If QD suppressors aren't for precision rifles... someone must have forgot to tell me.
Regarding cold bore / clean bore POI shift, I agree that cold bore shots will not exhibit a major difference in POI than the next 5 shots or until the barrel heats up to a point that will cause POI movement, which will happen eventually.
Now, CLEAN bore, as Mark pointed out, is another story. After using copper SOLVENT, you will likely see discernible POI movement. A way to minimize this is to use a product like KG-2, which is a bore polisher / micro abrasive that removes copper. Products like this remove copper fouling from the lands and grooves of the rifling only. The copper in the microscopic "terrain features" within the bore will remain. I've found KG's marketing claims to be absolutely true in this regard. There is no movement in point of impact after de-coppering the bore with KG-2.
Your experience may vary.
I'm very unlikely to use a "polish" or any kind of abrasive on my krieger barrels.
Leaving copper in the bore, no matter how small of an amount for an extended period of time is not a good idea.
Dissimilar metals behave badly when left to their own devices. This is why we clean barrels in the first place. Copper, when left to oxidize, will do bad things to any metal it is in contact with. Combine that with the amonia content of powder being burned at extremely high temperatures and pressures... and you've got a recipe for stainless steel to be turned into a sacrificial anode!
Do some research into why the military only uses chrome lined bores, and you'll understand more of what I'm talking about.
My rifles get cleaned when accuracy tapers off, or when I get up around 300-400rnds... OR when I'm going to not shoot them for a quite a while. When I do clean them... I want them CLEAN. Down to the metal. I want no copper or anything else in there. If I'm going to leave them sit for a while, I run an oiled patch down the tube. Otherwise I just dry patch, and go shoot them in and verify zero. Then they are ready to go.
Abrasive compounds and high end custom barrels? Not this guy.
Intentionally leaving copper (and who knows what else) in the bore when cleaning? Not this guy.
Whether it works or not, I don't much care. I know too much about metal behavior under harsh conditions to do that to a rifle I care about.
I'm not advocating using it all the time. Like you, I clean when accuracy drops off. And keep in mind that it's not like JB Bore paste. It's not nearly as abrasive.
I'm of the opposite persuasion, in that I will not introduce chemical solvents into my barrels any more than necessary.
I also disagree with your method of using a dry patch after cleaning with solvent before shooting. Shooting a bone dry, squeaky clean bore is an invitation for premature copper fouling. An oiled patch should be run down the bore after every cleaning session before shooting. You'll find that your mean time between cleanings will go up if you do this.
I understand that you are experienced, so I don't want you to take this difference of opinion as an insult. But so am I.
Even top tier barrel makers are divided on this issue. Look where Krieger, Bartlein, Gale Mcmillan, John Noveske etc. stand on these issues. They are divided.
Important part is that we're all knocking out the 10 ring. I will agree to disagree on this.
Have a good one.
You assume far too much about what I said.
I use patch out / wipe out. ... for lots of reasons that I don't feel like elaborating on right now. I'd hardly call it a harsh solvent. If I'm getting upwards of 500rnds of 308 before having to clean, I wouldn't think my method is somehow prematurely fouling.
I don't knock out the 10 ring. I rarely shoot paper. :)
This.
My rifles are always in a "fouled" condition. My custom barrels take as little as 3 rounds to come in, after being cleaned... while most of my factory barrels will take from 10-20.
This has been my experience as well and is why I never clean a bolt gun barrel that well.
A couple of patches of solvent and some dry patches and that is it.
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